Metalworking machine

ABSTRACT

A metalworking machine includes a tool for machining a workpiece metal and a cooling liquid supply unit for supplying a cooling liquid to a machining portion between the tool and the workpiece metal. The cooling liquid is formed by applying a degassing treatment that removes dissolved gases from the cooling liquid, and a hydrogenation treatment that adds hydrogen to the cooling liquid.

TECHNICAL FIELD

This invention relates to a metalworking machine and, in particular,relates to a metalworking machine that carries out metalworking withhigh precision for a short time.

BACKGROUND ART

Conventionally, as a working machine, there is known a lathe comprisinga main spindle base having a main spindle, a cutter base having amachining tool, a drive mechanism that drives the cutter base to movethe machining tool relative to a workpiece, and a cooling liquid supplymeans (nozzle) that supplies a cooling liquid to the machining tool andthe workpiece (see, e.g., Patent Document 1).

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP-A-2007-38323

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

Herein, when using the working machine described in Patent Document 1 tocut a workpiece metal such as an iron alloy or an Al alloy precisely fora short time (i.e. at high speed), it is necessary to carry outhigh-speed machining by moving the tool at high speed without causingany vibration or micro-vibration.

Then, as the machining speed increases, a machining portion between thetool and the workpiece metal generates more heat and therefore, it isnecessary to cool the machining portion by supplying a large amount ofcooling water or cooling liquid thereto.

As a consequence, the cooling liquid is supplied to the machiningportion at a pressure of about 10 kg/cm² to 30 kg/cm², but there hasbeen a problem that if the large amount of cooling liquid is supplied atsuch a high pressure, vibration is excited at the machining portion toadversely affect the precision machining.

The present applicant has elucidated the cause of the excitation ofvibration at the machining portion due to the supply of the coolingliquid and has obtained the following knowledge.

That is, atmospheric components (dissolved gases) are dissolved in anormal cooling liquid and, when the cooling liquid is transferred underpressure in a liquid supply pipe, a large amount of bubbles aregenerated.

The generated large amount of bubbles are repeatedly attached to anddetached from an inner wall of the liquid supply pipe. When the bubblesare adhered to the inner wall of the liquid supply pipe, thecross-sectional area through which the cooling liquid flows decreases sothat the pressure for flowing the cooling liquid increases, while, whenthe bubbles are released from the inner wall of the liquid supply pipe,the area through which the cooling liquid flows increases so that thepressure for flowing the cooling liquid decreases.

Since the large amount of bubbles repeat attachment to and detachmentfrom the inner wall of the liquid supply pipe in this manner, extremelysevere pressure oscillation occurs in the supply system of the coolingliquid.

Then, this oscillation is transmitted to the machining portion so thatvibration is excited at the machining portion.

On the other hand, when cutting/grinding an iron alloy or the like, oilis widely used as a cooling liquid in order to prevent oxidation of theworkpiece metal.

In this case, there has been a problem that when a large amount ofcooling liquid is required for high-speed machining, it is necessary todispose a large amount of waste oil and there has been a problem that itis necessary to clean a product after the machining, resulting in anincrease in workload.

Therefore, this invention is intended to solve the conventionalproblems, that is, it is an object of this invention to provide ametalworking machine that does not require waste oil disposal or productcleaning operation while preventing oxidation of a workpiece metal andthat prevents the occurrence of vibration at a machining portion evenwhen a large amount of cooling liquid is supplied thereto, therebyachieving metalworking with high precision and at high speed.

Means for Solving the Problem

A metalworking machine of the present invention comprises a tool formachining a workpiece metal and a cooling liquid supply means forsupplying a cooling liquid to a machining portion between the tool andthe workpiece metal, wherein the cooling liquid is formed by applying towater a degassing treatment that removes a dissolved gas and ahydrogenation treatment that adds hydrogen, and thus, resolved theforegoing problems.

Effect of the Invention

According to this invention, since a cooling liquid that is supplied toa machining portion is subjected to a degassing treatment that removes adissolved gas, it is prevented that bubbles are generated in a liquidsupply pipe when the cooling liquid is transferred under pressure in theliquid supply pipe, and therefore, it is possible to avoid theoccurrence of pressure oscillation in the supply system of the coolingliquid and thus to prevent this oscillation from being transmitted to amachining portion between a tool and a workpiece metal, therebyachieving metalworking with high precision and at high speed.

Since the dissolved gas is removed by applying the degassing treatmentto water, it is possible to easily dissolve hydrogen in the degassedwater.

By applying a hydrogenation treatment to the cooling liquid that issupplied to the machining portion, it is possible to lower theoxidation-reduction potential of the cooling liquid and thus to preventoxidation of the workpiece metal and, when the liquid supply pipe ismade of a metal, it is possible to prevent oxidation of the liquidsupply pipe.

By applying the degassing treatment to the water to remove the dissolvedgas, particularly an oxygen gas, as described above, the cooling liquidcan have a reducing property with the addition of only a small amount ofhydrogen.

The cooling liquid is mainly composed of at least the water and,therefore, it is possible to avoid the workload for waste oil disposalor product cleaning operation which is required when oil is employed asa cooling liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a metalworking machine according toan embodiment of this invention.

FIG. 2 is a schematic diagram mainly showing a cooling liquid supplymeans and a cooling water producing means.

FIG. 3 is a graph comparing vibration acceleration levels between purewater and gas-saturated water.

FIG. 4 is a graph showing relationships between the dissolved hydrogenconcentration and the oxidation-reduction potential.

FIG. 5A is an explanatory diagram for explaining an oscillation state ina liquid supply pipe in a machine stopped state.

FIG. 5B is an explanatory diagram for explaining an oscillation state ina liquid supply pipe when water added with hydrogen less than asaturated solubility is used.

FIG. 5C is an explanatory diagram for explaining an oscillation state ina liquid supply pipe when water added with hydrogen not less than asaturated solubility is used.

MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, a metalworking machine 100 according to an embodiment ofthis invention will be described with reference to the drawings.

Embodiment

First, the metalworking machine 100 according to the embodiment of thisinvention is a lathe and, as shown in FIGS. 1 and 2, comprises a mainspindle base 110 rotatably supporting a main spindle 111 that holds aworkpiece metal W, a tool base 120 provided movably with respect to themain spindle base 110 and the main spindle 111 and detachably supportinga tool 121, a cooling liquid supply means 130 for supplying a coolingliquid L to a machining portion A between the tool 121 and the workpiecemetal W, and a collecting tank 140 for storing the cooling liquid Lsupplied to the machining portion A.

As shown in FIG. 2, the cooling liquid supply means 130 is connected toa cooling water producing means 150, which produces the cooling liquidL, through a connecting pipe 160.

The metalworking machine 100 is configured to cut the workpiece metal Wusing the tool 121 by attaching the workpiece metal W to the mainspindle 111, attaching the tool 121 to the tool base 120, rotating themain spindle 111, and moving the tool base 120 to feed the tool 121 tothe workpiece metal W.

At the time of machining to cut off an unnecessary portion of theworkpiece metal W using the tool 121, the machining portion A betweenthe tool 121 and the workpiece metal W generates heat. Accordingly, inorder to ensure cooling and cutting machinability of the machiningportion A, the cooling liquid supply means 130 supplies the coolingliquid L to the machining portion A between the tool 121 and theworkpiece metal W.

As shown in FIG. 1, the cooling liquid supply means 130 comprises anozzle 131 for ejecting the cooling liquid L to the machining portion A,a liquid tank 132 for storing the cooling liquid L in an airtight state,a strainer (filter) 133 provided in the liquid tank 132, a liquid supplypipe 134 for supplying the cooling liquid L to the nozzle 131 from thestrainer 133, and a pump 136 driven by an electric motor 135.

As shown in FIG. 2, the cooling water producing means 150 comprises apretreater 151 for purifying raw water through a filter or a reverseosmosis membrane, a degassing cylinder 152 for removing dissolved gasesin the water purified by the pretreater 151, a moisture generator 153for generating steam in order to adjust an external environment of thedegassing cylinder 152, a gas dissolving cylinder 154 for addinghydrogen to the degassed water degassed by the degassing cylinder 152, araw water supply pipe 155 connected to the pretreater 151 for supplyingthe raw water thereto, a pure water supply pipe 156 connected betweenthe pretreater 151 and the degassing cylinder 152 for supplying purewater to the degassing cylinder 152, and a degassed water supply pipe157 connected between the degassing cylinder 152 and the gas dissolvingcylinder 154 for supplying the degassed water to the gas dissolvingcylinder 154.

Hereinbelow, a specific method of producing the cooling liquid L will bedescribed.

First, if atmospheric components (dissolved gases) are dissolved in thecooling liquid L (cooling water in this embodiment) up to the saturatedsolubility, a large amount of bubbles are inevitably generated when thecooling liquid L is transferred under pressure in the liquid supply pipe134.

Accordingly, first, city water (tap water) as raw water is purified to acertain degree in the pretreater 151 using the filter, the reverseosmosis membrane, or the like.

Then, from the water purified by the pretreater 151, atmosphericcomponents (dissolved gases) are removed in the degassing cylinder 152using a hollow fiber membrane (not illustrated).

Herein, in the degassing cylinder 152, the external environment of thehollow fiber membrane is reduced to a pressure of 20 to 30 Torr, therebyremoving a nitrogen gas (N₂) and an oxygen gas (O₂) from the waterpurified by the pretreater 151.

Specifically, steam is generated by catalytic reaction using a hydrogengas (H₂) and an oxygen gas in the moisture generator 153 and then issupplied to the outside of the hollow fiber membrane, thereby causingthe above-mentioned 20 to 30 Torr atmosphere to be an H₂O gas atmosphere(steam atmosphere) entirely.

When the pressure is reduced to 20 Torr to 30 Torr, dew condensationdoes not occur even in a 100% H₂O atmosphere.

When the water is passed through the degassing cylinder 152 in the H₂Ogas atmosphere, the N₂ and O₂ components in the water are reduced to 1ppb or less, respectively.

In atmospheric equilibrium, a nitrogen gas is 15 ppm and an oxygen gasis 8 ppm.

The contents of the oxygen gas and the nitrogen gas are required to be 1ppm or less, respectively, and are more preferably 1 ppb or less,respectively.

Herein, a graph of FIG. 3 shows the results of comparing vibrationacceleration levels between pure water (X1) in which the dissolvedoxygen concentration is suppressed to 1 μg/L or less by applying adegassing treatment thereto, and gas-saturated water (X2) whentransferred under pressure in the liquid supply pipe 134.

As is clear from this graph of FIG. 3, it has been found that when theultrapure water subjected to the degassing treatment is used, thevibration acceleration can be suppressed to 1 Gal or less.

Then, in order to set the oxidation-reduction potential of the degassedwater, in which the atmospheric components are degassed, to −0.4V tothereby eliminate oxidizability, the degassed water is introduced intothe gas dissolving cylinder 154 where hydrogen is added at 0.6 to 0.8ppm.

Specifically, hydrogen is supplied at high pressure to a hollow fibermembrane (not illustrated), thereby dissolving the hydrogen into thedegassed water flowing outside the hollow fiber membrane.

The saturated solubility of hydrogen at room temperature is 1.5 ppm.Therefore, in the case of the addition of hydrogen at about 0.6 to 0.8ppm, even if the cooling liquid L is transferred under pressure in theliquid supply pipe 134, no bubbles are generated at all in the liquidsupply pipe 134.

Herein, a graph of FIG. 4 shows the relationships between the dissolvedhydrogen concentration and the oxidation-reduction potential whenhydrogen is dissolved in ultrapure water.

Y1 shows a case where the dissolved oxygen concentration is 0.01 mg/L(0.31×10⁻⁶ mol/L), Y2 shows a case where the dissolved oxygenconcentration is 3 mg/L (0.09×10⁻³ mol/L), Y3 shows a case where thedissolved oxygen concentration is 10 mg/L (0.31×10⁻³ mol/L), and Y4shows a case where the dissolved oxygen concentration is 18 mg/L(0.56×10⁻⁶ mol/L).

As is clear from this graph of FIG. 4, it has been found that it ispossible to easily produce water having reducibility (having nooxidizability) only by controlling the gas concentration in theultrapure water.

When the dissolved oxygen content in the water is supersaturated orsaturated, the required hydrogen addition amount increases so that therearises a possibility of generation of bubbles due to hydrogen.

By degassing oxygen in the water, the water can have a reducing propertywith the addition of only a small amount of hydrogen, and therefore, itis possible to prevent both generation of bubbles due to oxygen gas andgeneration of bubbles due to hydrogen gas.

FIG. 5A is a graph measuring an oscillation state in the liquid supplypipe 134 in a machine stopped state, FIG. 5B is a graph measuring anoscillation state in the liquid supply pipe 134 when degassed wateradded with hydrogen less than a saturated solubility is used, and FIG.5C is a graph measuring an oscillation state in the liquid supply pipe134 when degassed water (hydrogen-supersaturated water) added withhydrogen not less than a saturated solubility is used.

As is clear from the graphs of FIGS. 5A to 5C, it has been found thatwhen the degassed water is added with hydrogen less than the saturatedsolubility, oscillation hardly occurs in the liquid supply pipe 134.

Since the cooling liquid L is a cooling liquid that is supplied to theultrahigh-speed machining portion A, it is effective to add degassedmineral oil or degassed oil and fat at several % (5%) to 10% in order toprovide a lubricating effect.

In this embodiment thus obtained, since the cooling liquid L that issupplied to the machining portion A is subjected to the degassingtreatment that removes the dissolved gases, it is prevented that bubblesare generated in the liquid supply pipe 134 when the cooling liquid L istransferred under pressure in the liquid supply pipe 134, and therefore,it is possible to avoid the occurrence of pressure oscillation in thesupply system of the cooling liquid L and thus to prevent thisoscillation from being transmitted to the machining portion A betweenthe tool 121 and the workpiece metal W, thereby achieving metalworkingwith high precision and at high speed.

Since the dissolved gases, particularly the nitrogen gas, are removed byapplying the degassing treatment to the water, it is possible to easilydissolve hydrogen in the degassed water thus obtained.

By applying the hydrogenation treatment to the cooling liquid L that issupplied to the machining portion A, it is possible to lower theoxidation-reduction potential of the cooling liquid L and thus toprevent oxidation of the workpiece metal W and, when the liquid supplypipe 134 or the connecting pipe 160 is made of a metal, it is possibleto prevent oxidation of the liquid supply pipe 134 or the connectingpipe 160.

By applying the degassing treatment to the water to remove the dissolvedgases, particularly the oxygen gas, the cooling liquid L can have areducing property with the addition of only a small amount of hydrogen.

The cooling liquid L is mainly composed of at least the water and,therefore, it is possible to avoid the workload for waste oil disposalor product cleaning operation which is required when oil is employed asthe cooling liquid L.

This invention is not limited to the above-mentioned embodiment and canbe changed within a range not departing from the gist of the invention.

For example, in the above-mentioned embodiment, the description has beengiven assuming that the metalworking machine is the lathe, but thisinvention may also be applied to a boring machine, a milling machine, ashaping machine, a grinding machine, and so on.

DESCRIPTION OF SYMBOLS

-   -   100 metalworking machine    -   110 main spindle base    -   111 main spindle    -   120 tool base    -   121 tool    -   130 cooling liquid supply means    -   131 nozzle    -   132 liquid tank    -   133 strainer    -   134 liquid supply pipe    -   135 electric motor    -   136 pump    -   140 collecting tank    -   150 cooling water producing means    -   151 pretreater    -   152 degassing cylinder    -   153 moisture generator    -   154 gas dissolving cylinder    -   155 raw water supply pipe    -   156 pure water supply pipe    -   157 degassed water supply pipe    -   160 connecting pipe    -   W workpiece metal    -   L cooling liquid    -   A machining portion

1. A metalworking machine comprising: a tool for machining a workpiecemetal; a supply unit for supplying a cooling liquid to a machiningportion between the tool and the workpiece metal; and a producing unitfor producing the cooling liquid by applying a degassing treatment thatremoves a dissolved gas from the cooling liquid and a hydrogenationtreatment that adds hydrogen to the cooling liquid.
 2. The metalworkingmachine according to claim 1, wherein the dissolved gas comprises anitrogen gas and an oxygen gas, and concentrations of the nitrogen gasand the oxygen gas dissolved in degassed water after the degassingtreatment are 1 ppm or less, respectively.
 3. The metalworking machineaccording to claim 2, wherein the concentrations of the nitrogen gas andthe oxygen gas after the degassing treatment are 1 ppb or less,respectively.
 4. The metalworking machine according to claim 1, whereinthe hydrogenation treatment is a treatment that adds the hydrogen in anamount which is less than a saturated solubility of the hydrogen andwhich reduces an oxidation-reduction potential of the cooling liquid toa numerical value having no oxidizability.
 5. The metalworking machineaccording to claim 4, wherein the hydrogenation treatment is a treatmentthat adds the hydrogen at 0.6 to 0.8 ppm.
 6. The metalworking machineaccording to claim 1, wherein the cooling liquid is formed by beingfurther subjected to an oil addition treatment that adds degassedmineral oil or degassed oil and fat.
 7. The metalworking machineaccording to claim 6, wherein the oil addition treatment is a treatmentthat adds the degassed mineral oil or the degassed oil and fat at 5 to10%.